Batteries are presently of particular interest both for mobile and stationary applications. So-called all-solid-state batteries contain exclusively solid materials, and in particular solid-state electrolytes, and in contrast to conventional batteries containing liquid electrolytes, they have several advantages.
The replacement of liquid electrolytes by solid-state electrolytes makes it possible, for example, to reduce the risk of a thermal runaway as well as an explosion of the battery and to increase the safety and the cycle stability of the battery.
However, a replacement of liquid electrolytes by solid-state electrolytes is normally accompanied by a reduction of the capacity of the cathode, since materials such as LiCoO2 have low lithium ion conductivity and only thin solid-state electrolyte films may be used in all-solid-state batteries.
To overcome this problem, Sakuda et al. in the Journal of Power Sources 2010 proposed a battery which includes a silicon anode, a Li2S.P2S5-solid-state electrolyte separator and a cathode made from a mixture of Li2S.P2S5 and LiNbO3—LiCoO2.
LiCoO2 is used in this case as an intercalation material into which lithium ions may be inserted during the charge process, and at the same time it functions as an electron conductor.
Li2S.P2S5 and LiNbO3 are used in this case as additives conducting lithium ions to compensate for the low lithium ion conductivity of LiCoO2.
However, LiCoO2 exhibits a volume expansion of 9% during the discharge process and a volume contraction of 9% during the charge process (see Dokko et al., Electrochem. Solid-State Lett. 3, 125, 2000).
This change in volume may, however, have the result that the contact between the LiCoO2 particles and Li2S.P2S5 or LiNbO3 is interrupted, causing the capacity of the battery to drop after several charge and discharge cycles.